Will the Plane Take-Off - Merged with MythBusters Show Thread
#203
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Originally Posted by wstevens
Why is a manhole cover round?
I'm so slow
#205
Yeehaw
You have 9 marbles: 8 of them weigh 1 ounce each; 1 weighs 1.1 ounce. The 9 marbles are all uniform in size, appearance and shape. You have access to a balance scale containing 2 trays - you may use the balance 2 times. You must determine which of the 9 marbles is the heavier one using the balance only 2 times.
#207
Yeehaw
this one is easier than the one in post #205:
You are given 5 bags. There are 10 beads in each of the bags. In four of the bags, the beads each weigh 10 kilograms. In the remaining bag, each bead weighs only 9 kilograms. All the bags and beads look identical. You must find out which bag has the lighter beads. The problem is that all the bags look identical and all the beads look identical. You can use a scale, but it has to be a single-tray scale, not a two-tray balance scale. Also, you may use the scale only once. How can you find out which bag has the lighter beads?
You are given 5 bags. There are 10 beads in each of the bags. In four of the bags, the beads each weigh 10 kilograms. In the remaining bag, each bead weighs only 9 kilograms. All the bags and beads look identical. You must find out which bag has the lighter beads. The problem is that all the bags look identical and all the beads look identical. You can use a scale, but it has to be a single-tray scale, not a two-tray balance scale. Also, you may use the scale only once. How can you find out which bag has the lighter beads?
#208
old school
Originally Posted by BEETROOT
this one is easier than the one in post #205:
You are given 5 bags. There are 10 beads in each of the bags. In four of the bags, the beads each weigh 10 kilograms. In the remaining bag, each bead weighs only 9 kilograms. All the bags and beads look identical. You must find out which bag has the lighter beads. The problem is that all the bags look identical and all the beads look identical. You can use a scale, but it has to be a single-tray scale, not a two-tray balance scale. Also, you may use the scale only once. How can you find out which bag has the lighter beads?
You are given 5 bags. There are 10 beads in each of the bags. In four of the bags, the beads each weigh 10 kilograms. In the remaining bag, each bead weighs only 9 kilograms. All the bags and beads look identical. You must find out which bag has the lighter beads. The problem is that all the bags look identical and all the beads look identical. You can use a scale, but it has to be a single-tray scale, not a two-tray balance scale. Also, you may use the scale only once. How can you find out which bag has the lighter beads?
#209
Yeehaw
Hmm yeah good point, I think that one got lost in translation somehow. The question I remember had the weights as 1 gram for the majority of the beads/marbles, and 1.1 for the other bag.
#210
old school
Originally Posted by BEETROOT
Hmm yeah good point, I think that one got lost in translation somehow. The question I remember had the weights as 1 gram for the majority of the beads/marbles, and 1.1 for the other bag.
#211
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Originally Posted by NSXNEXT
The car dyno is a good example. Is the car moving? No the wheels are. Is there air flowing over the hood of the car? No that's why they put the fans in front of the car to keep the engine temp cooler.
#213
wow this grew fast.
Eventually all of the engine power will be devoted to matching the resistance of the wheel bearings, leaving none to move the plane, and even if there was more, the treadmill would match it anyway.
Mike
Eventually all of the engine power will be devoted to matching the resistance of the wheel bearings, leaving none to move the plane, and even if there was more, the treadmill would match it anyway.
Mike
#214
Nom Nom Nom Nom
Originally Posted by crazymjb
wow this grew fast.
Eventually all of the engine power will be devoted to matching the resistance of the wheel bearings, leaving none to move the plane, and even if there was more, the treadmill would match it anyway.
Mike
Eventually all of the engine power will be devoted to matching the resistance of the wheel bearings, leaving none to move the plane, and even if there was more, the treadmill would match it anyway.
Mike
#216
What you guys are all forgetting is that this is not a frictionless environment.
It does take more force to move the plane when the wheels are spinning in the opposite direction. Put a toy with wheels on a treadmill(something heavy), attatch a pull scale. As the speed goes up the pull in the opposite direction will increase. Now, pull on the scale... Yes the plane will move forward, but it now takes the amount of force to hold the plane from flying backwards plus the force to pull the plane forward. Again, the faster it goes, the more that resistance factor goes up. So eventually, since the treadmill has an unlimeted top speed, it will overcome the power of the engines.
You are correct in saying it has nothing to do with the wheels creating propulsion, but there is a rearward pull.
Hers another example: Put a fan on the back of a toy car that is light enough to be blow forward. Now measure the speed of the toy car and place it on a treadmill going that speed, the power from the fan will now be devoted to overcoming the resistance from the wheel bearings, requiring the fan to be turned up to move the car forward. Turbines have a maximum RPM until they fail, whereas our hypothetical treadmill doesnt.
I win
Mike
It does take more force to move the plane when the wheels are spinning in the opposite direction. Put a toy with wheels on a treadmill(something heavy), attatch a pull scale. As the speed goes up the pull in the opposite direction will increase. Now, pull on the scale... Yes the plane will move forward, but it now takes the amount of force to hold the plane from flying backwards plus the force to pull the plane forward. Again, the faster it goes, the more that resistance factor goes up. So eventually, since the treadmill has an unlimeted top speed, it will overcome the power of the engines.
You are correct in saying it has nothing to do with the wheels creating propulsion, but there is a rearward pull.
Hers another example: Put a fan on the back of a toy car that is light enough to be blow forward. Now measure the speed of the toy car and place it on a treadmill going that speed, the power from the fan will now be devoted to overcoming the resistance from the wheel bearings, requiring the fan to be turned up to move the car forward. Turbines have a maximum RPM until they fail, whereas our hypothetical treadmill doesnt.
I win
Mike
#219
The problem is you are putting an unconstrained variable (the treadmills speed, and hence the force being put on the plane to go the other direction) against a contrained variable (the maximum output of the jets engines.
Lets have some math/aeronatical wiz calculate at what speed the treadmill would be moving for a 747 or any plane for the thrust of the engines to no longer be able to counter the force being applied by the engines. I believe it would be setup by setting the maximum power output of the engines equal to bearing resistance and the airliners weight along with tire stickiness(may be negligable).
And I couldn't agree more that this would be very interesting to see done on a smaller scale at M5 Industries.
Mike
Lets have some math/aeronatical wiz calculate at what speed the treadmill would be moving for a 747 or any plane for the thrust of the engines to no longer be able to counter the force being applied by the engines. I believe it would be setup by setting the maximum power output of the engines equal to bearing resistance and the airliners weight along with tire stickiness(may be negligable).
And I couldn't agree more that this would be very interesting to see done on a smaller scale at M5 Industries.
Mike
#220
Yeehaw
Originally Posted by crazymjb
The problem is you are putting an unconstrained variable (the treadmills speed, and hence the force being put on the plane to go the other direction) against a contrained variable (the maximum output of the jets engines.
Last analogy...
You have a toy truck on a treadmill. There is a rope tied to this truck. You are holding the rope, standing in front of the treadmill.
When you pull that rope, does it make any difference how fast the treadmill is going? Would you have to pull 50 times harder if the treadmill was spinning at 50mph than if it was spinning at 1mph?
The answer is no, it wouldn't make any difference. The force of you pulling the rope is independent of the spinning treadmill and the spinning wheels of the truck. Just like the thrust of the jet engine is completely independent of the spinning treadmill on the runway.
#222
Try this. Put a toy truck on the treadmill. Attatch the a rope to the truck over a pully and to a bucket. As the treadmill speed increases the truck will go back pulling the bucket up. Put some sand into the bucket, it will now require more speed for teh truck to pull the bucket up, but it will still do so. That sand is independant of the treadmill. The more sand added the more "thrust" used. at a certain point the bucket will become fill, and no more sand can be added, but as long as you can keep increasing the speed of the treadmill, the truck will continue to be able to be pushed back.
I am emailing Mythbusters BTW.
Mike
I am emailing Mythbusters BTW.
Mike
#223
Yeehaw
dude, a truck on a treadmill would not pull any harder as the speed of the treadmill went up. Perhaps a tiny bit from friction, but not enough to be significant.
#224
Ok... Get a toy truck, fill it with 300 lbs of weights, attatch it to a string and to your nutsack. Turn on treadmill. When you get out of the hospital, tell me how the resistance is insignificant.
It is important to remember at speed all resistance is significant, especially when that speed is limitless.
You are at least admitting that there is some resistance... But you are stating it is negligable. .00000000001 *10^X can be significant if X is high enough. With a treadmill with no top speed, X = Infiniti. So the plane could never keep up, and hence, never take off.
Mike
It is important to remember at speed all resistance is significant, especially when that speed is limitless.
You are at least admitting that there is some resistance... But you are stating it is negligable. .00000000001 *10^X can be significant if X is high enough. With a treadmill with no top speed, X = Infiniti. So the plane could never keep up, and hence, never take off.
Mike
#225
Yeehaw
Let me get this straight. Your argument is that at what...a million rpm?... the friction of the ball bearings in a wheel would be so great it would be stronger than the jet engines, thereby canceling out their force and stopping the plane from moving? And this would be caused by the extra rpms generated by the <200 mph speed the plane needs to take off?
Lets keep it within the bounds of reality.
Lets keep it within the bounds of reality.
#226
Interesting. Interesting.
Originally Posted by crazymjb
So now you are placing bets... The amount of friction will go up until the bearings cook and sieze.
Mike
Mike
You know how small this bearing friction is compared to the thrust of an airplane engine? Negligable doesn't begin to describe it. It's a non issue.
#227
You know what I may be thinking...
That the treadmill is spinning fast enough to keep the jet in the same position at full thrust(Which is possible, on paper anyway) while you are simply stating it is spinning the exact speed the wheels are but in the opposite direction.
But then I'm still right because...
However, by doing that, it would increase wheel speed, and in turn have to increase its own speed, making its speed increase infinatly until the plane wasn't moving...
So I still win
Mike
That the treadmill is spinning fast enough to keep the jet in the same position at full thrust(Which is possible, on paper anyway) while you are simply stating it is spinning the exact speed the wheels are but in the opposite direction.
But then I'm still right because...
However, by doing that, it would increase wheel speed, and in turn have to increase its own speed, making its speed increase infinatly until the plane wasn't moving...
So I still win
Mike
#228
Interesting. Interesting.
Originally Posted by crazymjb
You are at least admitting that there is some resistance... But you are stating it is negligable. .00000000001 *10^X can be significant if X is high enough. With a treadmill with no top speed, X = Infiniti. So the plane could never keep up, and hence, never take off.
Mike
Mike
Also, if you're point is that a small percentage of a large number is still a large number, I agree with that. However, we're talking about the vector sum of forces here. If the vector sum doesn't equal zero, then the plane will move.
#229
Interesting. Interesting.
Originally Posted by crazymjb
You know what I may be thinking...
That the treadmill is spinning fast enough to keep the jet in the same position at full thrust(Which is possible, on paper anyway) while you are simply stating it is spinning the exact speed the wheels are but in the opposite direction.
But then I'm still right because...
However, by doing that, it would increase wheel speed, and in turn have to increase its own speed, making its speed increase infinatly until the plane wasn't moving...
So I still win
Mike
That the treadmill is spinning fast enough to keep the jet in the same position at full thrust(Which is possible, on paper anyway) while you are simply stating it is spinning the exact speed the wheels are but in the opposite direction.
But then I'm still right because...
However, by doing that, it would increase wheel speed, and in turn have to increase its own speed, making its speed increase infinatly until the plane wasn't moving...
So I still win
Mike
#231
Interesting. Interesting.
Originally Posted by mclarenf3387
The only true issue I could see if this were a real situation would probably be the tires exploding from the heat.
Last edited by wstevens; 08-18-2006 at 08:08 PM.
#233
Interesting. Interesting.
Originally Posted by crazymjb
If a plane has full brakes on its not taking off... So the tires exploding and/or the bearings melting would more or less simulate that situation...
Mike
Mike
(b) if a plane has it's tire brakes on (as opposed to air brakes on the wings), full thrust of the engines would cause the tire brakes to fail. Easily.
#235
(a) Melting bearing results in siezing. How To: Overtighten a wheel bearing on your car fill grease cover with sand.
(b) If you have a plane on a runway, you have the wheel brakes locked, and power up from there, the plane will not take off. I know this is definatly true with a prop driven plane, and I know that 747s are not supposed to remain at 100% Power for more than 20 seconds or the tarmack(sp?) starts coming up... I assume that means they are able to stay still.
Mike
(b) If you have a plane on a runway, you have the wheel brakes locked, and power up from there, the plane will not take off. I know this is definatly true with a prop driven plane, and I know that 747s are not supposed to remain at 100% Power for more than 20 seconds or the tarmack(sp?) starts coming up... I assume that means they are able to stay still.
Mike
#236
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The question centers around a force independent of the wheels being able to drive the plane forward on a perfect treadmill - The closest I've come to agreeing with Rootbeer is the argument that the wheels will just spin faster as the plane accelerates because the thrust is applied independent of the forces of the treadmill.
Try this experiment.
Attach your toy truck to a winch that will draw the truck across the floor at 5 mph (simulating thrust as the force moving the truck is independent of the wheels).
Now place this truck on a treadmill going 5 mph in the opposite direction and activate the winch. Does the truck move relative to the earth (ie, could it generate lift if it had wings?) I don't think so, I don't care what straight dope says, my non physics mind can't reason it out just yet. I'll start drinking and make a new formulation later.
Now, if that truck were already in the air, then it would move at 5 mph relative to the earth - I think.
Try this experiment.
Attach your toy truck to a winch that will draw the truck across the floor at 5 mph (simulating thrust as the force moving the truck is independent of the wheels).
Now place this truck on a treadmill going 5 mph in the opposite direction and activate the winch. Does the truck move relative to the earth (ie, could it generate lift if it had wings?) I don't think so, I don't care what straight dope says, my non physics mind can't reason it out just yet. I'll start drinking and make a new formulation later.
Now, if that truck were already in the air, then it would move at 5 mph relative to the earth - I think.
#237
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It seems like the sum of the forces acting on the plane (treadmill vs forward thrust) is zero in a perfect system. Arguing about ball bearings or tires failing is missing the forest for the trees.
I am trying to reason out what would happen if the conveyor/treadmill were a passive system - ie free spinning but not actively being driven. I am inclined to believe that the plane would be able to fly in such a system.
I am trying to reason out what would happen if the conveyor/treadmill were a passive system - ie free spinning but not actively being driven. I am inclined to believe that the plane would be able to fly in such a system.
#238
Interesting. Interesting.
Originally Posted by crazymjb
(a) Melting bearing results in siezing. How To: Overtighten a wheel bearing on your car fill grease cover with sand.
(b) If you have a plane on a runway, you have the wheel brakes locked, and power up from there, the plane will not take off. I know this is definatly true with a prop driven plane, and I know that 747s are not supposed to remain at 100% Power for more than 20 seconds or the tarmack(sp?) starts coming up... I assume that means they are able to stay still.
Mike
(b) If you have a plane on a runway, you have the wheel brakes locked, and power up from there, the plane will not take off. I know this is definatly true with a prop driven plane, and I know that 747s are not supposed to remain at 100% Power for more than 20 seconds or the tarmack(sp?) starts coming up... I assume that means they are able to stay still.
Mike
(a) so it seizes...so what? does that mean that any amoun of force can't move it? Once you have wheel lock you can't move the vehicle no matter how much for you apply? Nope..all that will happen is the wheels will be dragged by the thrust....and the plane will still take off.
(b) How do you know this is definitely true for prop planes? and I have no idea what you mean by tarmac "coming up"
Last edited by wstevens; 08-18-2006 at 09:36 PM.
#239
Interesting. Interesting.
Originally Posted by Gpump
It seems like the sum of the forces acting on the plane (treadmill vs forward thrust) is zero in a perfect system. Arguing about ball bearings or tires failing is missing the forest for the trees.
I am trying to reason out what would happen if the conveyor/treadmill were a passive system - ie free spinning but not actively being driven. I am inclined to believe that the plane would be able to fly in such a system.
I am trying to reason out what would happen if the conveyor/treadmill were a passive system - ie free spinning but not actively being driven. I am inclined to believe that the plane would be able to fly in such a system.
Most airplane wheels are passive. Planes cannot move unless their engines are producing thrust.
#240
Interesting. Interesting.
Originally Posted by crazymjb
(a) Melting bearing results in siezing. How To: Overtighten a wheel bearing on your car fill grease cover with sand.
(b) If you have a plane on a runway, you have the wheel brakes locked, and power up from there, the plane will not take off. I know this is definatly true with a prop driven plane, and I know that 747s are not supposed to remain at 100% Power for more than 20 seconds or the tarmack(sp?) starts coming up... I assume that means they are able to stay still.
Mike
(b) If you have a plane on a runway, you have the wheel brakes locked, and power up from there, the plane will not take off. I know this is definatly true with a prop driven plane, and I know that 747s are not supposed to remain at 100% Power for more than 20 seconds or the tarmack(sp?) starts coming up... I assume that means they are able to stay still.
Mike
And by the way, our of curiosity, what are you basing any of your info on? Stuff you;ve actually learned? or just stuff you "think" is true?